The invention relates to filaments for toothbrushes.
Breuer et al., U.S. Pat. No. 4,802,255, which is hereby incorporated by reference, describes nylon monofilaments that include at least two colored regions, one of which is provided by a dye. The monofilaments are included in the bristles of toothbrushes and, as the toothbrush is used by the owner, the color intensity of the dyed region changes in response to wear, providing an indication of when the toothbrush should be replaced. Breuer et al. lists six food dyes or colorants that can be used to dye the monofilaments, including Indigotine (FD&C Blue No. 2), and in col. 4 broadly describes the conditions that can be used for dyeing. Breuer et al. also provides a number of specific examples of dyeing procedures, including three (examples 4-6) in which Indigotine is used as the dye.
The specific dyeing procedures described by Breuer et al. were for laboratory samples. However, to produce a sufficient amount of dyed filaments for commercial toothbrushes, a procedure is needed that can be used for dyeing large amounts of filaments. The procedure should be cost-efficient and, of course, should produce nylon filaments that have a consistent level of dye penetration.